1. Field of the Invention
The present invention relates to pipettors generally and, more particularly, but not by way of limitation, to a novel pipettor especially useful in transferring small volumes of liquid.
2. Background Art
In the field of biotechnology, there has been a constant effort to increase the quantity of bioassay-type experiments. This is particularly true in the specific areas of xe2x80x9chigh throughput screeningxe2x80x9d for new drugs and human genome research. As the volume of tests increases, so does the corollary of costs. Tests that were originally done in 16 mm test tubes, moved to 96 tests at a time in the microplate format (8xc3x9712 wells on 9 mm centers). Now, there is increased interest in further miniaturization in a 384-well format. In the same size as the microplate (3.3xe2x80x3xc3x975xe2x80x3), there are 384 wells in a 16 by 24 array on 4.5 mm centers. The individual well volume decreases from approximately 300 microliters per well in the microplate down to less than 100 microliters per well. The resulting benefit is reduced usage of the costly reagents used in testing.
The tight spacing of a 384-well plate, 4.5 mm center-to-center plate, essentially eliminates the possibility of manual pipetting, due to the very tedious effort involved. The conventional automated X-Y-Z bridge pipettors can be used, but they are limited to from 1 to 8 needles at a time, again due to the physical limitation of 4.5 mm center-to-center spacing. Thus there is clearly a need for a faster method of transferring liquid samples to and from such wells.
There are three basic considerations which must be addressed. First, since small volumes (i.e., less than 100 microliters) are to be pipetted, accuracy and precision of delivery is required. Second, in most applications, carryover between samples must be eliminated, or at the least, minimized. Third, the tight spacing between wells presents sealing problems and force problems that do not exist on the larger scale of 9 mm center-to-center spacing such as used in microplates.
Accordingly, it is a principal object of the present invention to provide a small volume pipettor which provides accuracy and precision of delivery of liquid samples.
It is a further object of the invention to provide such a small volume pipettor in which carryover between samples is minimized or eliminated.
It is an additional object of the invention to provide such a small volume pipettor which overcomes the sealing problems and force problems inherent in simultaneously pipetting a large number of liquid samples.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.
The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a small volume pipettor, comprising: a plurality of pistons; a plurality of liquid delivery needles; motive means to cause one of said pistons to move axially within one of said needles to cause a liquid to be selectively drawn into and discharged from said needle; sealing means disposed around said pistons to effect sealing of upper ends of said needles; assembly means in which said needles and said sealing means are disposed; and means to permit said assembly means to be removed from said pipettor as a one-piece unit. Further provided are novel means to seal upper ends of said needles around said pistons.